Method and means for detection of gases and vapors



April 23, 1968 MIKIYA YAMANE 3,379,968

METHOD AND mums FOR DETECTION 0E GASES AND VAPORS Original Filed Oct. 9,1963 2 Sheets-Sheet 1 G RECORDER I? I38 I? HIGH ELECTRO- HIGH VOLTAGEMETER VOLTAGE SOURCE AMPLIFIER SOURCE I ---FI owMETER-- GAS SEPARATIONCOLUMN ARG ON GAS TANK ELECTROMETER 8 ELECTROMETER -|8 AMPLIFIERAMPLIFIER l 1 HIGH VOLTAGE HIGH VOLTAGE SOURCE SOU RCE April 1968 MlKlYAYAMANE 3,379,968

METHOD AND MEANS FOR DETECTION OF GASES AND VAPORS 2 Sheets-Shee 2SENSING CHAMBER ANODE VOLTAGE United States Patent 3,379,968 METHOD ANDMEANS FOR DETECTIGN 0F GASES AND VAPORS Mikiya Yamane, 27 of 201Kunitachi, Kunitachi-machi, Kitatama-gun, Tokyo-to, Japan Continuationof application Ser. No. 315,011, Oct. 9, 1963. This application Aug. 7,1967, Ser. No. 658,949 Claims priority, application Japan, Oct. 13,1962, 37/ 45,419 4 Claims. (Cl. 324-33) The application is acontinuation of my copending application Ser. No. 315,011, filed Oct. 9,1963, now abandoned.

This invention relates to a method and means for detecting minuteconcentrations of gases and vapors in gas chromatographic analysis, andmore specifically it relates to an improvement of the method of theargon ionization detector.

The argon ionization detector, which was developed by J. E. Lovelock,has heretofore been used widely as a highly sensitive detector for gaschromatography. In this detector a radioactive source is contained, andargon as the carrier gas is ionized by the high-velocity ionizingparticles radiated from this radioactive source to generate primaryelectrons. These primary electrons are accelerated by a voltage appliedbetween the anode and the cathode of the detector, thereby gainingenergy, and collide with argon atoms to produce metastable argon atoms.If a minute quantity of other gases and vapors exists, the metastableargon atoms can transfer their energies to these gases and vapors,leading to their ionization when the potential of the metastable atom ishigher than the ionization potentials of the gas or vapor molecules. Bymeasuring the ionization current which is produced in this manner, it ispossible to detect these gases and vapors.

This conventional argon detector described above can be modified byreplacing the radioactive source by a gaseous discharge which is excitedin the vicinity of the sensing electrodes.

It is an object of the present invention to provide a method and circuitwhich can supply etiectively a copious stream of electrons from such adischarge in order to increase the sensitivity of the detector.

The nature, principle, and details of the invention, as well as themanner in which the said and other objects of the invention may best beachieved, will be most clearly apparent by reference to the followingdescription of a preferred embodiment of the invention when read inconjunction with the accompanying drawings, in which like parts aredesignated by like reference characters, and in which:

FIGURE 1 is a schematic diagram, partly as a block diagram, showing thecompositional arrangement of a gas chromatograph wherein a gas detectioncircuit according to the invention is used;

FIGURE 2 is schematic diagram, as a sectional view, showing theconstruction of the detector of the gas chromatograph shown in FIGURE 1;

FIGURES 3 and 4 are schematic circuit diagrams showing states of voltageapplication on the discharge electrodes of the detector shown in FIGURE2; and

FIGURE 5 is a graphical representation showing curves respectivelyindicating the relationships between the anode voltage and thebackground current of the gas detection circuit of the invention in thecases of the states indicated in FIGURES 3 and 4.

In the gas chromatograph shown by the schematic diagram of FIGURE 1, inwhich the gas detection circuit of the invention is incorporated, thereis provided a first flow path in which argon is used as a carrier3,379,968 Patented Apr. 23, 1968 ice gas, and which comprises a tank 1for storing argon gas for separating the sample gas, a flow regulatingvalve 2, a sample inlet line 3, and a column 4 for separating the samplegas. In addition, there is provided a second flow path I; which is forcausing flow of helium gas and causing subsidiary discharge to takeplace within this flow, and which comprises a helium tank 5 and a flowregulating valve 6. These two flow paths a and b are connected to adetector 7, whose gas outlet flow is measured by a fiowmeter 8.

The detector 7, which is shown in detail in relatively enlarged view inFIGURE 2, comprises a sensing chamber 10, a discharge chamber 9communicating with the sensing chamber 10, an inlet 11 for introducingdischarge gas into the discharge chamber 9, an inlet 12 for introducingcarrier gas into the sensing chamber 10, a common gas outlet 13 forexhausting gases from the sensing chamber 10, a pair of dischargeelectrodes 14 consisting of two metal wires mounted in the dischargechamber 9, and a semispherical cathode 16 and a tubeshaped anode 17provided in mutually confronting disposition in the sensing chamber 10.

The discharge electrodes 14 are connected to a high voltage source 15shown in FIGURE 1 and are adapted to accomplish D.C. discharge ofseveral tens of microamperes of discharge current. The cathode 16 andanode 17 are respectively connected to a recorder 22 by way of anelectrometer amplifier 18 and to a high voltage source 19 as indicatedin FIGURE 1.

In the operation of the detector 7, a portion of the electrons generatedby the discharge in the discharge chamber 9 flows into the sensingchamber 10, is accelerated in the gap between the cathode 16 and anode17, and ionizes the sample gas injected through the anode 17. Theresulting ionized current is measured by the electrometer amplifier 18connected to the cathode 16.

The sensitivity of this detection system has a relationship to themagnitude of the ionizing current, and, furthermore, the ionizingcurrent is proportional to the number of electrons flowing from thedischarge chamber 9 into the sensing chamber 10.

The gas detection circuit of the present invention is designed to supplya large quantity of primary electrons from the discharge chamber 9 intothe sensing chamber 10 by accomplishing discharge by means of a highvoltage source of negative polarity and, at the same time, impressing ahigh positive voltage on the anode 17 in the sensing chamber 10, andthereby to increase the sensitivity of detection of the system.

In order to indicate still more fully the nature of the invention, theoperation and effectiveness of the detection circuit of the invention isdescribed hereinbelow with respect to a preferred embodiment of theinvention.

FIGURE 3 is a schematic diagram indicating the case wherein thedischarge within the discharge chamber 9 of the invention isaccomplished by means of a highvoltage source of negative polarity,while FIGURE 4 is a diagram indicating the case wherein the discharge isaccomplished by means of a high-voltage source of positive polarity. Ineach of FIGURES 3 and 4, the highvoltage source and a current limitingresistor connected in series are respectively designated by referencenumerals 20 and 21.

Under each of the circuit conditions as indicated in FIGURES 3 and 4,the discharge of 30 microamperes was accomplished in a stream of heliumof a fiowrate of cc./rnin. by means of the high-voltage source 20, andmeasurements were made with argon used as the carrier gas flowing at aflowrate of 60 cc./ min. The relationships between the measuredbackground currents and the respective anode voltages for the two casesindicated in 3 FIGURES 3 and 4 are indicated by curves 1 and 2,respectively, shown in FIGURE 5. These two cases will be consideredseparately in greater detail hereinbelow.

( 1) The case in which the discharge is excited by a negativehigh-voltage source As can be observed in FIGURES 3 and 5, whendischarge is caused, by means of a negative power source, with onedischarge electrode grounded and the other electrode at a potential ofminus 270 volts (resulting from a voltage of 870 volts of the powersource 20 and a voltage drop of 600 volts across the current limitingresistor 21), the space potential in the vicinity of the electrodes 14is negative. Accordingly, when the anode voltage is zero volt, thepotential of the sensing chamber is zero, which is higher than thepotential of the discharge chamber 9. Consequently, the electronsproduced are attracted to the cathode 16 and the anode 17, and anegative current flows to the electrometer amplifier 18.

When the anode voltage becomes several tens of volts,

7 the potential of the sensing chamber 10 becomes high.

Consequently, the number of electrons attracted increases. However,since most of these electrons are collected at the anode 17, the numberof electrons moving to the cathode 16 becomes less. When the anodevoltage reaches several hundreds of volts, the number of electrons drawninto the sensing chamber 10 increases even further, but all of theseelectrons are collected at the anode 17, and a small quantity of ionsgenerated by photo-ionization and other causes flow to the cathode 16.Consequently, a positive current flows to the electrometer amplifier 18.Accordingly, this state conforms to the ideal condition whereinelectrons necessary for ionizing the sample gas collect at the anode 17which is injecting the sample gas, and, moreover, the background currentis very low.

Next, when the anode voltage is caused to be of the order of minus 50volts, most of the electrons drawn into the sensing chamber 19 collectat the cathode 16, and a large negative current flows to theelectrometer amplifier 18. When the anode voltage is further lowered,the potential of the sensing chamber 10 becomes low, tending to suppressthe flow of electrons. Consequently, the number of electrons flowing tothe cathode 16 decreases, and, at the same time, ions begin to flow tothe anode 17. Accordingly, the electron current to the electrometeramplifier 18 is reduced. When the anode voltage is lowered still furtherand recahes a value of the order of minus 1,000 volts, ions are drawninto the sensing chamber and flow to the anode 17, and electrons such assecondary electrons due to photo-ionization flow to the cathode 16.

(2) The case in which the discharge is excited by a positivehigh-voltage source As can be observed in FIGURES 4 and 5, whendischarge is caused, by means of a positive power source, with onedischarge electrode grounded and the other electrode at a potential ofplus 270 volts (resulting from a voltage of 870 volts of the powersource 20 and a voltage drop of 600 volts across the current limitingresistor 21), the space potential in the vicinity of the electrodes 14is positive. Since, at the same time, the cathode 16 of the sensingchamber 10 is grounded by way of an input resistor (not shown) of theelectrometer amplifier 18, it may be considered to be at approximatelythe ground potential. Accordingly, when the anode voltage is zero volt,the potential of the sensing chamber 10 is zero, which is lower than thepotential of the discharge chamber 9, and positive ions created by thedischarge are drawn by the force of the electric field. Although theflow of electrons is also to be expected at this time, the quantity ofions is relatively greater. These ions flow to the anode 17 and thecathode 16, wherefore a positive current flows to the electrometeramplifier 18.

When the anode voltage becomes approximately 50 volts, the ions aredrawn into the sensing'chamber 10, but in the interior of the sensingchamber, the ions are repelled by the anode 17 and fiow to the cathode16. Accordingly, a large positive current flows to the electrometeramplifier- 18. When the anode voltage is further increased, thepotential of the sensing chamber becomes high, tending to suppress theflow of ions, and the quantity of ions flowing to the cathode 16 isreduced. At the same time, electrons begin to flow to the anode 17, andthe reading of the electrometer amplifier 18 becomes less. The ioncurrent decreases with increase in the anode voltage. When the anodevoltage eXceeds'LOOO volts, ionization of the electrons flowing to theanode begins. Accordingly, the quantity of ions flowing to the cathode16 increases once again.

Next, when the anode voltage becomes negative, the potential of thesensing chamber 10 becomes negative, and a large quantity of ions flowsinto the sensing chamber 10. However, since the greater portion of theseions flows to the anode 17, the current flowing to the electrometeramplifier 18 decreases. When the anode voltage is further lowered, anegative current flows to the electrometer amplifier 18. Although thisindicates that electrons are flowing to the cathode 16, this indicationis believed to be due to electrons such as secondary electrons emittedby the impact of ions against the anode 17 and electrons generated byphoto-ionization.

As will be apparent from the foregoing disclosure, the backgroundcurrent is determined by the relationship between the potentials of thedischarge chamber 9 and the sensing chamber 10 and by the relationshipbetween the potentials of the cathode and anode within the sensingchamber. It is to be observed that by carrying out discharge with anegative power source and, at the same time, impressing a positive highvoltage on the anode, electrons necessary for ionization of the samplegas are supplied at a high rate, and, moreover, an ideal operationalcondition wherein the background current is low is obtained.Accordingly, the gas detection method and circuit according to thepresent invention, wherein such an ideal condition is realized, ishighly effective in practical applications, particularly in increasngsensitivty of measurements by gas chromatography.

It should be understood, of course, that the foregong disclosure relatesto only a preferred embodiment of the invention and that it is intendedto cover all variations and modifications of the example of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention as setforth in the appended claims.

What is claimed is:

1. A device for detecting gases and vapors by ionization due toirradiation of primary electrons generated by the ionization action ofan electric discharge, comprising a discharge chamber; a sensing chamberconnected to said discharge chamber by a constricted and concentricallyaligned connector; a pair of discharge electrodes disposed in saiddischarge chamber in mutually opposed position facing in the directionof said connector; a first power source; one of said electrodes beingconnected to the negative terminal of said first power source; the otherelectrode being grounded; a discharge gas inlet leading into saiddischarge chamber in the direction of its center axis; a carrier gasinlet leading in the direction of the center axis of said sensingchamber for the introduction of a sample gas therein; an anode and anopposing cathode disposed in said sensing chamber; a second powersource; said anode being connected to the positive terminal of saidsecond power source; said cathode being connected to a circuit formeasuring electric current due to ionization of said sample gas; and gasoutlet means from said discharge chamber and said sensing chamber.

2. The device as defined in claim 1, wherein said gas outlet means are acommon outlet leading out of said sensing chamber opposite saidconnector.

3. A process for the detection of gases and vapors by ionization due toirradiation of primary electrons genertaed by the ionization action ofan electric discharge, comprising the steps of introducing a dischargegas into a discharge chamber provided with a pair of mutually opposedelectrodes, one of said electrodes being connected to the negativeterminal of a first power source, the other being grounded; causing anelectric discharge to occur between said electrodes; injecting primaryelectrons generated by said electric discharge into a sample gasintroduced into a sensing chamber adjacent to said discharge chamber andconnected thereto by a constricted and coaxially aligned connector; saidsensing chamber being provided with an anode and an opposing cathode,said anode being connected to the positive terminal of a second powersource; said sample gas being ionized betwen said cathode and saidanode; said cathode being connected to a circuit which measures theelectric current caused to flow by the ionization of said sample gas.

4. The process as defined in claim 3, wherein said discharge gas ishelium and said carrier gas is argon.

References Cited RUDOLPH V. ROLINEC, Primary Examiner.

C. F. ROBERTS, Assistant Examiner.

1. A DEVICE FOR DETECTING GASES AND VAPORS BY IONIZATION DUE TOIRRADIATION OF PRIMARY ELECTRONS GENERATED BY THE IONIZATION ACTION OFAN ELECTRIC DISCHARGE, COMPRISING A DISCHARGE CHAMBER; A SENSING CHAMBERCONNECTED TO SAID DISCHARGE CHAMBER BY A CONSTRICTED AND CONCENTRICALLYALIGNED CONNECTOR; A PAIR OF DISCHARGE ELECTRODES DISPOSED IN SAIDDISCHARGE CHAMBER IN MUTUALLY OPPOSED POSITION FACING IN THE DIRECTIONOF SAID CONNECTOR; A FIRST POWER SOURCE; ONE OF SAID ELECTRODES BEINGCONNECTED TO THE NEGATIVE TERMINAL OF SAID FIRST POWER SOURCE; THE OTHERELECTRODE BEING GROUNDED; A DISCHARGE GAS INLET LEADING INTO SAIDDISCHARGE CHAMBER IN THE DIRECTION OF ITS CENTER AXIS; A CARRIER GASINLET LEADING IN THE DIRECTION OF THE CENTER AXIS OF SAID SENSINGCHAMBER FOR THE INTRODUCTION OF A SAMPLE GAS THEREIN; AN ANODE AND ANOPPOSING CATHODE DISPOSED IN SAID SENSING CHAMBER; A SECOND POWERSOURCE; SAID ANODE BEING CONNECTED TO THE POSITIVE TERMINAL OF SAIDSECOND POWER SOURCE; SAID CATHODE BEING CONNECTED TO A CIRCUIT FORMEASURING ELECTRIC CURRENT DUE TO IONIZATION OF SAID SAMPLE GAS; AND GASOUTLET MEANS FROM SAID DISCHARGE CHAMBER AND SAID SENSING CHAMBER.